In the windowless basement of a Manhattan church last month, Bellevue Hospital hosted a fashion show.

Dozens of weight-loss surgery patients, some in evening gowns, strutted down a red carpet. While their “before” photos were projected on a screen, an M.C. read testimonials about how the operations had remade their lives.

Addressing the cheering crowd, Bellevue’s chief medical officer boasted about a remarkable number. The overwhelmed public hospital, which routinely treats gunshot and stabbing wounds, was on track to perform a record 3,000 weight-loss surgeries this year.

“We have a lot to be proud of,” the executive, Dr. Nathan Link, said.

Bariatric surgery is a major operation that, for the right patients, can ward off heart disease, diabetes and strokes. Bellevue, which serves a disproportionately poor and obese population, says the operations have saved many lives.

But a New York Times investigation found that the bariatric program, led by surgeons with financial incentives to perform more operations, has become a high-speed assembly line that has endangered some patients and compromised urgent care for others. And because most of the hospital’s patients are on Medicaid or uninsured, taxpayers foot the bill.

The surgery shrinks patients’ stomachs and requires them to radically change how and what they eat. Even some successful operations can lead to a lifetime of stomach cramps and debilitating acid reflux.